The term "Yersinia enterocolitica" as used herein, refers to the bacteria classified as such Bergey's Manual of Systematic Bacteriology (N. R. Krieg [ed.], 1984, 498-506, Williams & Wilkins). Detection of Yersinia enterocolitica (Y. enterocolitica) is important in various medical and public health contexts. Yersinia enterocolitica infection can cause a variety of symptoms ranging from those resembling a cold to gastroenterocolitis. Under-cooked or uncooked meats are frequently a source of human food-borne infection from these organsims but routine screening is both time consuming and difficult.
It is, therefore, an aspect of the present invention to provide a novel assay system capable of rapidly detecting Yersinia enterocolitica and which is generally applicable to environmental, food or clinical samples.
Pursuant to a standard laboratory method and method recommended by the F.D.A. (FDA/BAM Bacteriological Analytical Manual, Chapter 11, 6th Edition, 1984, Supplement 9/87', Association of Offical Analytical Chemist), the presence of Yersinia enterocolitica in environmental or dairy specimens (e.g., milk) has been traditionally detected by culturing an appropriately prepared sample on microbiological media under conditions favorable for growth of these organisms. The resulting colonies are then typically examined for morphological and biochemical characteristics, a process that generally is initiated 48 hours after acquisition of the sample and disadvantageously takes between 12-17 days to complete.
It is yet another aspect of the present invention to avoid the disadvantage associated with traditional culturing techniques and to employ nucleic acid probes to detect Yersinia enterocolitica.
It is yet another aspect of the present invention to provide probes which can hybridize to target regions which can be rendered accessible to the probes under normal assay conditions.
While Kohne et al. (1968) Biophyscial Journal 8:1104-1118 discuss one method for preparing probes to rRNA sequences they do not provide the teaching necessary to make Yersinia enterocolitica specific probes.
Pace and Campbell (1971) Journal of Bacteriology 107:543-547 discuss the homology of ribosomal ribonucleic acids from diverse bacterial species and a hybridization method for quantitating such homology levels. Similarly, Sogin, Sogin, and Moese (1972) Journal of Molecular Evolution 1:173-184 discuss the theoretical and practical aspects of using primary structural characterization of different ribosomal RNA molecules for evaluating phylogenetic relationships.
Fox, Pechman, and Moese (1977) International Journal of Systematic Bacteriology discuss the comparative cataloging of 16S ribosomal RNAs as an approach to prokaryotic systems. These references, however, fail to relieve the deficiency of Kohne's teaching with respect to Yersinia enterocolitica.
Ribosomes are of profound importance to all organisms because they serve as the only Known means of translating genetic information into cellular proteins, the main structural and catalytic elements of life. A clear manifestation of this importance is the observation that all cells have ribosomes.
Ribosomes contain three distinct RNA molecules which, at least in E. coli, are referred to as 5S, 16S, and 23S rRNAs. These names historically are related to the size of the RNA molecules, as determined by sedimentation rate. In actuality, however, they vary substantially in size between organisms. Nonetheless, 5S, 16S, and 23S rRNA are commonly used as generic names for the homologous RNA molecules in any bacteria, and this convention will be continued herein.
Hybridization is traditionally understood as the process by which, under predetermined reaction conditions, two partially or completely complementary single-stranded nucleic acids are allowed to come together in an antiparallel fashion to form a double-stranded nucleic acid with specific and stable hydrogen bonds. The stringency of a particular set of hybridization conditions is defined by the base composition of the probe/target duplex, as well as by the level and geometry of mispairing between the two nucleic acids. Stringency may also be governed by such reaction parameters as the concentration and type of ionic species present in the hybridization solution, the types and concentrations of denaturing agents present, and/or the temperature of hybridization. Generally, as hybridization conditions become more stringent, longer probes are preferred if stable hybrids are to be formed. As a corollary, the stringency of the conditions under which a hybridization is to take place (e.g., based on the type of assay to be performed) will largely dictate the preferred probes to be employed. Such relationships are well understood and can be readily manipulated by those skilled in the art. As a general matter dependent upon probe length, such persons understand stringent conditions to mean approximately 35.degree. C.-65.degree. C. in a salt solution of approximately 0.9 molar.
As used herein, probe(s) refer to synthetic or biologically produced nucleic acids (DNA or RNA) which, by design or selection, contain specific nucleotide sequences that allow them to hybridize under defined predetermined stringencies, specifically (i.e., preferentially) to target nucleic acid sequences.
A target nucleic acid sequence is one to which a particular probe capable of preferentially hybridizing.
Still other useful definitions are given as their first use arises in the following text. All references cited herein are fully incorporated by reference.